PROJECT SUMMARY/ABSTRACT Increased moderate-to-vigorous intensity physical activity (MVPA) is associated with reductions in treatment- related side effects, cancer recurrence and mortality, and increased QOL in breast and endometrial cancer survivors. However, the majority (~70%) of survivors do not meet cancer-specific MVPA recommendations (i.e., 150 mins/week). MVPA support is not part of standard care, resulting in few survivors having access to efficacious MVPA programs. Failure to translate MVPA programs into care is a result of most interventions being intense, on-site programs that deliver multiple components simultaneously to all participants. This ?one- size-fits-all? approach does not account for individual needs, nor can it realistically be implemented into survivorship care. mHealth tools (i.e. smartphone applications, Fitbits, text messages), are inexpensive and have demonstrated efficacy for increasing MVPA in other populations. Thus, they may be a more scalable, less resource-intensive strategy to increase MVPA in more survivors. The ability to integrate wearable MVPA monitor data into the electronic health record (EHR) further enhances the potential for a technology-supported MVPA intervention to be integrated into cancer care. However, responses to these tools are heterogeneous and may vary as part of a gradually progressing (in terms of weekly goal mins) MVPA program and their effects on morbidity indicators is unknown. While a minimal intervention including the Fitbit integrated into the EHR (Fitbit+EHR) may be sufficient for some cancer survivors to increase their MVPA, others will need more support. Further, some survivors may need this additional support early on, while others may succeed early, but fail later when the MVPA goal increases. Evidence is lacking to determine: a) whether the best augmentation tactic for increasing MVPA in non-responders is to offer another mHealth component (i.e. online exercise videos) alone or with a more traditional component (i.e., telephone coaching) and b) what the best adaptive intervention is to improve morbidity indicators. Thus, we propose to utilize a novel adaptive intervention design to determine the optimal: 1) augmentation component(s) to address non-response and 2) adaptive intervention for improving morbidity indicators (i.e., symptom burden and functional performance). Inactive breast and endometrial cancer survivors (n=320) will receive a Fitbit integrated into the EHR (Fitbit+EHR). Those who do not respond to the Fitbit+EHR intervention as evidenced by failure to sufficiently increase their MVPA will be re-randomized to one of two subsequent augmentation tactics, either: (1) online gym or (2) online gym and coaching calls. Responders will continue with the Fitbit+EHR for 6 months. The project is significant because it aims to develop an effective and scalable MVPA intervention for cancer survivors that will move from a one-size-fits-all approach to a dynamic, tailored approach for MVPA promotion by identifying non-responders at the right time and providing them with the additional intervention components necessary to increase MVPA and improve health and disease outcomes.